1. Field of the Invention
The present invention relates to a sewing machine provided with a needle bar and a looper which are driven respectively by individual actuators.
2. Discussion of the Related Art
A conventional electric sewing machine is provided with a single motor for driving both an arm shaft for vertically moving a needle bar, and a lower shaft for rotating a looper. In such a conventional electric sewing machine with a single motor, the motor drives the arm shaft, and the rotation of the upper shaft is transmitted through a transmission mechanism to the lower shaft.
The transmission mechanism interlocking the arm shaft and the lower shaft places restrictions on the general basic construction and design of the electric sewing machine. Furthermore, the transmission mechanism requires much time and labor for fine adjustment in assembling the same so that the arm shaft and the lower shaft operate synchronously to enable the looper to catch a loop of a needle thread.
A sewing machine proposed to deal with such problems is provided with individual motors respectively for driving the arm shaft and the lower shaft.
In this sewing machine with individual motors, the arm shaft and the lower shaft are mechanically independent of each other, and the arm shaft and the lower shaft are driven individually by a needle-bar driving system and a lower-shaft driving system, respectively. Accordingly, if the needle-bar driving system or the lower-shaft driving system is moved unnecessarily by vibrations (for example, as may occur when the sewing machine is moved) or the like before the electric sewing machine is connected to a power source, the positional relation between the needle bar and the looper is disturbed and, consequently, the looper is unable to catch a loop of the needle thread or the looper interferes with the needle so that the electric sewing machine is unable to form stitches.